When a blackout or the like occurs during operation of a computer, various troubles such as data loss and system failure occur. Thus, there is an uninterruptible power supply device that stably supplies power to a load (a computer, etc.) even when a sudden blackout occurs. Patent Document 1 (identified below) discloses an uninterruptible power supply device that performs stable power supply to a load by continuing power supply from a secondary battery to the load during stop of a power supply unit that supplies power to the load.
The uninterruptible power supply device described in Patent Document 1 includes a secondary battery that supplies power to a load; and a plurality of power supply units connected in parallel. Moreover, each power supply unit limits an output current to a predetermined value, has constant power drooping characteristics of drooping an output voltage when it is necessary to output an output current equal to or higher than the predetermined value, and controls output power to be constant. Each power supply unit supplies power to the load and also charges the secondary battery. The uninterruptible power supply device calculates maximum output power for one power supply unit, sets the maximum output power value for each power supply unit, and controls the constant power drooping characteristics of each power supply unit.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-154552.
However, when the load is an information processing system device, such as a server, a voltage drop may cause unstable operation. Therefore, the power supply device in Patent Document 1 having constant power drooping characteristics is not suitable as a power supply device for an information processing system device such as a server.